In recent years, the means of communication has diversified. Various kinds of communication have become available, including not only conventional voice communication but also video communication, text communication (mail, instant message, chat, and the like), file-sharing communication, whiteboard-sharing communication, and application-sharing communication.
Moreover, when communication systems are provided to users for such kinds of communication, cases have emerged in which, instead of all communication systems being put together in one type of terminal, a part (one or more) of types of terminal is used in combination in accordance with features of the terminals.
For example, a communication system that requires, like video communication, a high resolution and a moving image processing capability is offered as application on PC (Personal Computer); a communication system that can have a lower processing capability like voice communication but requires stability is offered on a dedicated terminal like a telephone.
When a plurality of terminals are used appropriately as described above, the terminals that the same user uses are often linked to each other by inputting into the terminals an ID that identifies a user, such as a user ID, to provide a sense of usability that makes the user feel that the user uses one terminal.